Differential ultrasonic waveguide cure monitoring probe

ABSTRACT

The present invention is seen to provide a new methodology, testing system designs and concept to enable in situ real time monitoring of the cure process. Apparatus, system, and method for the non-destructive, in situ monitoring of the time dependent curing of advanced materials using one or more differential ultrasonic waveguide cure monitoring probes. A differential ultrasonic waveguide cure monitoring probe in direct contact with the material to be cured and providing in situ monitoring of the cure process to enable assessment of the degree of cure or cure level in a non-cure related signal variances (e.g., temperature) independent calibrated response manner. A differential ultrasonic waveguide cure monitoring probe including a transducer coupled to a waveguide and incorporating correction and calibration methodology to accurately and reproducibly monitor the cure process and enable assessment of cure level via ultrasonic reflection measurements. The amplitude of the corrected interface response signal reflected from the probe-resin interface indicating changes in the modulus of the material during the cure.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 12/481,141 filed Jun. 9, 2009, which claims thebenefit of U.S. Provisional Patent Application 61/059,982 filed Jun. 9,2008, the disclosure of which are being incorporated herein by referencein their entirety.

TECHNOLOGY FIELD

The present invention relates generally to the real time, in situmonitoring of materials undergoing a cure process, and moreparticularly, to a differential ultrasonic waveguide cure monitoringprobe for monitoring of the cure process for materials that undergo acure process to enable assessment of cure level via ultrasonicreflection measurements in a reproducible, environmentally stable,temperature independent calibrated response manner.

BACKGROUND

Cure monitoring and assessment of the cure completion is performed viaextensive application of many technologies. Most conventionaltechnologies require testing of witness coupons or samples cut out fromthe structure. Testing of witness coupons or actual samples of thematerial being cured is not real time and is an inaccurate means ofassessing cure state of the actual structure material. Samplingmethodology does not always result in satisfactory assessment of thecuring conditions of the structure. For example, localized samples fromlarger polymer or composite structures often are not representative ofthe actual cure state of the material resulting in incomplete orunsatisfactory cure information.

In situ cure monitoring, among others, has been performed via variousmeans, including optical, electrical, electromagnetic, mechanical andultrasonic methods. Ultrasonic methods, for example, provide anadvantage of directly sensing the mechanical modulus change of thecuring material and thus directly monitor the structural cure of thematrix material. Widely demonstrated in a variety of curingapplications, conventional ultrasonic measurements required to monitorand quantify the degree of cure can be cumbersome, expensive andrequires complex set up and calibration procedures that make theapplication of this technology impractical for everyday use. Simple,real time and reproducible in situ cure monitoring is a significantproblem facing many manufacturing applications. Current methodologiesare inadequate for practical and economic ultrasonic cure monitoringneeds for various cure applications, such as aerospace, civil, marineand related industries.

Several patents describe ultrasonic techniques for cure monitoring andsome explore ultrasonic reflection for the potential cure monitoring.For example, U.S. Pat. Nos. 5,009,104 and 6,644,122 describe ultrasoniccure monitoring and evaluation of advanced materials and composites.Further, there is a group of ultrasonic cure patents that utilize timeof flight (ultrasonic wave transit time) or signal loss (attenuation)measurement approaches (see e.g., U.S. Pat. Nos. 4,455,268; 4,515,545;4,559,810; 5,911,159; 6,675,112) to monitoring materials modulus andcure state. Furthermore, embedded thin waveguide sensors explore cureeffects on the waveguide walls and corresponding change to acousticalsignal in and around different configuration waveguides (see e.g., U.S.Pat. Nos. 5,911,159; 4,904,080; 4,574,637; 4,590,803; and U.S. PatentPublication No. 2006/0123914). Some methodologies explore acousticalresonance (e.g., U.S. Pat. No. 4,758,803). Although physically correct,these approaches are entirely impractical and difficult to implementbecause of extensive and expensive tooling needs for multipletransducer, general loss of transducer after each process and the needto accurately measure transducer separation distances and ultrasonicwave travel times. U.S. Pat. No. 6,644,122 is directed to an ultrasoniccure monitoring process and describes a very general approach to curemonitoring; however this reference does not describe a sensingfunctionality or measurement process and simply states that theultrasound responds to cure processes as a measurement tool. A majorityof other patents, such as U.S. Pat. Nos. 7,245,371; 4,891,591 and4,874,948 rely on other indirect sensing technologies that utilizenon-mechanical, physically different means of estimating cure. However,none of the noted patents describe or teach a reproducible, differentialand calibration approach of cure monitoring as in the embodiments of thepresent invention. Without the simplification of the testconfigurations, implementation of differential probes and implementationof calibration methods—the cure level measurements are arbitrary andhave very limited engineering and applications value.

The present inventor's initial experiments utilizing ultrasonic cureusing direct reflection coefficient (as reported in B. Boro Djordjevic“Cure Monitoring by Ultrasonic Reflection Coefficient”, Proc.SAMPE-ACCE-DOE, September 27-28, Detroit, Mich. 1999 and B. BoroDjordjevic, B Milch “In-situ Ultrasonic Cure Monitoring Sensors” Proc.43 Int'l SAMPE 98 Symposium, pp 967-967, May 31-July 4, Anaheim Calif.1998) were successful in identifying an ultrasonic cure process, butimpractical because of the unpredictable influence and variances innon-cure related signal variances, such as variances in temperatureeffects, variances in pressure effects, variances in transducerresponse, variances in waveguide response, and unspecified variances ininstruments calibration effects that did not allow quantitativeassessment of cure affected ultrasonic reflection signals and madeimpossible true comparison of the material cure level.

What is needed is a system and method that uses a direct, differentialand calibrated approach for in situ monitoring of materials undergoing acure process to ensure practical, reproducible, and comparablemeasurements of the cure process and degree of cure.

SUMMARY

There has been summarized above, rather broadly, the prior art that isrelated to the present invention in order that the context of thepresent invention may be better understood and appreciated. In thisregard, it is instructive to also consider some of the objects andadvantages of the present invention.

It is an object of the present invention to provide an improvedmonitoring of the cure process via direct ultrasonic means that enabledirect, reproducible and calibrated estimate of the materials' degree ofcure.

It is another object of the present invention to provide in situmonitoring of the cure during materials' processing operations thusminimizing process errors and subsequent requirements to test state ofthe cure completion.

It is yet another object of the present invention to enable automatecalibration and estimate of the cure material modulus change, cureprocess materials modulus changes and final material cure state inreproducible and comparative engineering manner.

It is a further object of the present invention to provide a method andapparatus including signal processing requirements and cure probearrangements that enable ultrasonic reflection based cure monitoringtests in a variety of materials manufacturing operations such as andincluding, among others: autoclave composite manufacturing, vacuumbagged oven cure and resin transfer molding composite manufacturing.

It is still a further object of the present invention to provide genericmethodology to provide means to automatically maintain real time cureprocess information and enable use of this information by the cureprocessing apparatus and especially enable real time cure processtracking and cure process optimization to prevent and predict problemsand failures.

These and other objects and advantages of the various embodiments of thepresent invention will become readily apparent as the invention isbetter understood by reference to the accompanying summary, drawings andthe detailed description that follows.

Recognizing the need for the development of improved apparatuses,systems, and methods for materials cure monitoring, the presentinvention is generally directed to satisfying the needs set forth aboveand overcoming the disadvantages identified with prior art devices andmethods.

In accordance with the present invention, the foregoing need can besatisfied by providing an in situ differential ultrasonic waveguideprobe that enables real time monitoring of materials cure state viaultrasonic reflection measurements in a non-cure related signalvariances (e.g., temperature) independent calibrated response manner.

According to one embodiment of the invention, a differential ultrasonicwaveguide cure monitoring probe is provided for in situ ultrasonicmonitoring of a material undergoing a cure process. The differentialultrasonic waveguide cure monitoring probe includes an ultrasonictransducer connected to a waveguide. The waveguide includes a proximalend in contact with the ultrasonic transducer and a distal end forcontacting the material undergoing the cure process. The waveguide alsoincludes a first portion extending from the proximal end, a reference,and a second portion extending from the reference to a tip at a distalend of the waveguide. An ultrasonic signal may be generated by theultrasonic transducer and transmitted into the waveguide. An interfacesignal may be generated by a portion of the ultrasonic signal reflectingback from the interface of the probe and the material undergoing a cure.The interface signal is reflected back to the ultrasonic transducer andis used to directly sense the mechanical modulus change of the curingmaterial. A reference signal may be generated by a portion of theultrasonic signal reflecting back from the reference. The referencesignal is reflected back to the ultrasonic transducer and may be used torecalibrate the probe and account for non-cure related signal variancesduring the cure process. A quantitative assessment of a cure level ofthe material undergoing the cure process may be determined in a non-curerelated signal variances independent calibrated response manner usingthe reference signal to correct/recalibrate the interface signal.

According to one aspect of the invention, the reference of thedifferential ultrasonic waveguide cure monitoring probe includes one of:a cross-sectional reference; a slot reference; a small transducercross-section reference; an insert/void reference.

According to another aspect of the invention, the differentialultrasonic waveguide cure monitoring probe comprises an alternategeometry, the alternate geometry including an angled body wherein thesecond portion of the waveguide extends at an angle relative to thefirst portion of the waveguide.

According to another aspect of the invention, the differentialultrasonic waveguide cure monitoring probe is in direct contact with thematerial undergoing the cure process, the probe is only connected to oneside of the material being cured, and the cure monitoring is performedin situ to allow real time monitoring of the cure process.

According to another aspect of the invention, the differentialultrasonic waveguide cure monitoring probe is initially calibratedbefore the cure process begins using a material having knowncharacteristics and wherein the probe is continuously calibrated duringthe cure process using the reference signal to account for non-curerelated signal variances during the cure process in order to providequantitative assessment and comparison of cure rates and degree of curecompletion.

According to another embodiment of the invention, an in situ method formonitoring the cure of a curable material is disclosed. The methodincludes initially calibrating the differential ultrasonic waveguidecure monitoring probe by reference to the final from a material having aknown impedance. The differential ultrasonic waveguide cure monitoringprobe may then be coupled to a material to be cured, the differentialultrasonic waveguide cure monitoring probe comprising an ultrasonictransducer and a waveguide extending from the ultrasonic transducer. Thedifferential ultrasonic waveguide cure monitoring probe may bepositioned with a tip and front face of the waveguide in direct contactwith the material to be cured. The method continues with generating apulse of ultrasound energy using the ultrasonic transducer and directingthe pulse of ultrasound energy through the waveguide toward the materialbeing cured. A portion of the ultrasound energy is reflected back from areference structure of the waveguide and a portion of the ultrasoundenergy is reflected back from a materials boundary interface between theprobe and the material being cured. The ultrasound energy reflected fromthe materials boundary interface between the probe and the materialbeing cured may be sensed, as well as the ultrasound energy reflectedfrom the reference. The method provides for correcting the sensedultrasound energy reflected from the materials boundary interface usingthe sensed ultrasound energy reflected from the reference. As a result,a real time measurement of the modulus of the material being cured at aparticular point in the curing process may be determined using thesensed ultrasound energy reflected from the materials boundary interfaceand from the reference.

According to another aspect of the invention, the step of sensing theultrasound energy reflected from the materials boundary interfacefurther comprises: analyzing the amplitude of the reflected ultrasoundenergy from the materials boundary interface and the reference;periodically analyzing the amplitude of the waveform of the reflectedultrasound energy from the materials boundary interface to determinewhether the modulus of the composite has reached a predeterminedmodulus; and terminating the cure process once the predetermined modulusis reached.

According to another aspect of the invention, the step of correcting themeasurement further comprises continuous in situ non-cure related signalvariances compensation of the ultrasound energy reflected from thematerials boundary interface using the ultrasound energy reflected fromthe reference to ensure accurate and reproducible sensing of the curematerial during the cure process.

According to another aspect of the invention, the step of correcting themeasurement further comprises continuous in situ temperaturerecalibration of the ultrasound energy reflected from the materialsboundary interface using the ultrasound energy reflected from thereference to ensure accurate and reproducible sensing of the curematerial during the cure process.

According to yet another aspect of the invention, a series of pulses ofultrasound energy, and corresponding reflected reference signals andreflected interface signals, are generated and sensed over a period oftime at predetermined time intervals.

According to another embodiment of the invention, a differentialultrasonic waveguide cure monitoring system is provided. The systemincludes a differential ultrasonic waveguide cure monitoring probecoupled to a computer. The differential ultrasonic waveguide curemonitoring probe includes: an ultrasonic transducer for generating andsensing ultrasonic signals; a waveguide connected to and extending fromthe ultrasonic transducer; the waveguide for transmitting ultrasonicsignals; a reference for reflecting a reference signal back to theultrasonic transducer; and a front face of the waveguide for contactinga material to be cured and forming an interface between the differentialultrasonic waveguide probe and the material to be cured; the interfacereflecting back an interface signal from the interface to the ultrasonictransducer. The computer may include: an input device for receivinginformation relating to the reference signal and the interface signal; aprocessor for analyzing the information relating to the reference signaland the interface signal, and for distinguishing the propagationdifferences between the response signal and the interface signal toestimate the cure material modulus to determine a quantitative curestate of the material in a non-cure related signal variances independentcalibrated response manner; a data storage device for storing one ormore of: the information relating to the reference signal and theinterface signal, information relating to the material being cured, andinformation relating to the cure process; and an output device foroutputting one or more of: the information relating to the referencesignal and the interface signal, information relating to the materialbeing cured, and information relating to the cure process.

According to one aspect of the invention, the differential ultrasonicwaveguide cure monitoring probe may be integrated into new computerizedcure process monitoring system. According to another aspect of theinvention, the differential ultrasonic waveguide cure monitoring probemay be retrofit into existing materials processing assemblies. Further,tooling mounting options may be provided for coupling the differentialultrasonic waveguide cure monitoring probe to the material to be cured.

Thus, there has been summarized above, rather broadly, the presentinvention in order that the detailed description that follows may bebetter understood and appreciated. There are, of course, additionalfeatures of the invention that will be described hereinafter and whichwill form the subject matter of any eventual claims to this invention.Additional features and advantages of the invention will be madeapparent from the following detailed description of illustrativeembodiments that proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofpreferred embodiments, is better understood when read in conjunctionwith the appended drawings. For the purpose of illustrating theinvention, there is shown in the drawings exemplary constructions of theinvention; however, the invention is not limited to the specific methodsand instrumentalities disclosed. Included in the drawings are thefollowing Figures:

FIG. 1 shows an exemplary system and test bed set up including adifferential ultrasonic waveguide cure monitoring probe connected to amaterials to cure and a computer system;

FIG. 2 shows an exemplary measurement set up, for the ultrasonic curesensor illustrating the sensing interface between a material being curedand a waveguide probe;

FIG. 3 is a graph showing exemplary critical ultrasonic parametersgoverning signal interactions at the probe-resin interface defining arelative reflection coefficient (R_(RRC)) value;

FIG. 4 shows an exemplary and simplified embodiment of the ultrasonicprobe, including an ultrasonic transducer and a waveguide sensingextension that provides a sound reflection path for interface signalsensing used for cure monitoring and reference signal sensing used forin situ continuous probe calibration;

FIG. 5 is a graph showing an exemplary R_(RRC) signal response duringcure of polyester resin at room temperature and environment indicatingstages of the cure cycle;

FIG. 6 is a graph showing R_(RRC) versus time for the proper cure of anexemplary fiberglass/polystyrene resin composite during processindicating stages of the cure cycle;

FIG. 7 is a graph showing insufficient cure sensed by response of theR_(RRC) signal from the cure sensor in an exemplaryfiberglass/polystyrene resin composite during process indicatinginsufficient solidification of the material during final stages of thecure cycle;

FIGS. 8A-8E show different embodiments of an ultrasonic probe includingan ultrasonic transducer and a waveguide attachment having a waveguidetype reference;

FIGS. 9A-9D show an exemplary cure probe having a cross-sectionreference;

FIGS. 10A-10D show an exemplary cure probe having a slot reference;

FIGS. 11A-11D show an exemplary cure probe having a small transducercross-section reference;

FIGS. 12A-12D show an exemplary cure probe having a collar couplingconnecting the ultrasonic transducer to the waveguide member;

FIG. 13 shows an exemplary cure probe having an alternative waveguidegeometry;

FIGS. 14A-14C show exemplary ultrasonic transducers;

FIG. 15 is a block diagram showing exemplary system hardware, includingan A/D board, a pulser/receiver card, and a channel multiplexer board;

FIG. 16 is a graph showing an exemplary rectified ultrasonic signalshowing initial pulse, reference echo, and cure interface echo for anexemplary probe having a slot reference;

FIG. 17 is a graph showing exemplary RF signals for reference echo andcure sensing interface echo for an exemplary probe having a cut or slotreference;

FIG. 18 is a graph showing a generic waveguide ultrasonic waveformsignal for an exemplary 2 inch long PMMA probe with drive and reflectedair signal from the probe test interface;

FIG. 19 is a graph showing an exemplary ultrasonic record of a 2.25 MHzsignal for an exemplary 1.389 inch long PMMA probe with a slotreference;

FIG. 20 is a flow chart illustrating an exemplary relative reflectioncoefficient (RRC) cure monitoring process;

FIG. 21 is an exemplary system showing the cure probe coupled to a PChaving multiplexing, signal processing, and automated data collectionand processing;

FIG. 22 is an exemplary screen shot of the display of the PC of FIG. 21;

FIG. 23 is a block diagram of an example computing environment in whichan example embodiment may be implemented;

FIG. 24 shows exemplary tooling mounting options, including a siliconerubber skirt;

FIG. 25 shows exemplary tooling mounting options, including a hardmounting option;

FIG. 26 shows exemplary tooling hard mounting options with solid toolingproviding ultrasonic wave path to the interface probe;

FIG. 27 shows an exemplary schematic design of a multi-element curesensing interface critical angle reflection probe;

FIG. 28 shows an exemplary single element critical angle reflectionprobe; and

FIG. 29 shows another exemplary critical angle reflection probe havingmulti-site surface reflection geometry at the waveguide cure sensinginterface termination.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Before explaining various embodiments of the present invention indetail, it is to be understood that the invention is not limited in itsapplication to the details of construction and to the arrangements ofthe components set forth in the following description or illustrated inthe drawings. The invention is capable of other embodiments and of beingpracticed and carried out in various ways. For example, the preferredembodiments disclosed herein are directed to monitoring resins cure;however, it should be understood that these monitoring and detectiontechniques are applicable to a wide range of structural materials andprocesses. Also, it is to be understood that the phraseology andterminology employed herein are for the purpose of description andshould not be regarded as limiting.

Fabrication of large composite structures with thermosetting polymersrequires an understanding of the overall cure cycle, including localcure rates and degree of cure completion. As described supra, there iscurrently no effective manufacturing method to in situ monitorvisco-elastic and mechanic changes in the resin during cure process.During the cure, a thermo-set resin undergoes changes in viscosity,mechanical modulus, density, and ultrasonic velocity. During a curecycle, the resin material becomes more rigid and starts to behave as asolid. Cured resin has an increased ability to support longitudinal andshear waves with corresponding increased stiffness.

Also described supra, ultrasonic waves have been demonstrated as aneffective way to measure the cure process. However, most of theconventional ultrasonic NDE methods are cumbersome, complex and requireadvanced signal interpretation. The differential ultrasonic waveguidecure monitoring probe of the present invention uses known ultrasonicmaterial (e.g., in the form of a waveguide) coupled into the organicresin and accurately measures changes in signal reflection/transmissiondue to impedance change in the curing resin. Further, the probe contactinterface can be optimized for specific resins to enhance signals andquantitatively track the resin cure cycle.

The following describes the basic physic and measurement conceptsassociated with the ultrasonic waveguide interface signal reflectionmeasurements. Also described are exemplary processes and modes ofoperation of improved differential ultrasonic waveguide in situ curemonitoring probe for the reliable and inexpensive manufacturing processcontrol of resin, filled resin, fiber reinforced organic matrixcomposites, and the like. Many composite structures manufacturingoperations have need for rugged and inexpensive NondestructiveEvaluation (NDE) sensors suitable for factory and in-field cure processmonitoring. Embodiments of the present invention use a differentialultrasonic waveguide cure monitoring probe that is based uponmeasurement of an ultrasonic Relative Reflection Coefficient (RRC)derived from normalized and differentially corrected UltrasonicReflection Coefficient (URC) measurement at the probe resin interface.The differential ultrasonic waveguide cure monitoring probe measurementprocess enables calibrated and reproducible cure monitoring.

Although a well known physical phenomena, in practice reproduciblemeasurements of the ultrasonic interface reflections are difficult tomeasure. The practical quantitative monitoring of the interface signalis required to achieve a reproducible cure monitoring process. Thereproducibility of the URC measurements is influenced by several factorsor non-cure related signal variances, including the materials, theultrasonic transducers, temperatures, pressures and instrumentationconditions. To achieve URC waveguide probe reproducible calibration overmany possible operating conditions, the probe/sensor must measure theacoustic impedance change across a material boundary interface andcorrects/recalibrates this measurement to reference factors built intothe sensing probe.

By performing initial signal calibration on the differential ultrasonicwaveguide cure monitoring probes and continuous non-cure related signalvariances compensations, the differential ultrasonic probe arrangementcan reproducibly sense the full cure cycle of the resins. Because thedifferential ultrasonic waveguide cure monitoring probe responds tochanges in resin density and sound velocity, the degree of cure can bequantitatively calibrated to determine the cure-state. The differentialultrasonic waveguide cure monitoring probe, integrated with automateddata collection system, enables novel in-process composite curemonitoring.

Embodiments of the present invention relate to probes, systems, andmethods associated with technology for the in situ ultrasonic monitoringof the cure process of a material that undergo a cure process (e.g.,polymer composites and related materials with matrix material). Adifferential ultrasonic waveguide cure monitoring probe is conceived toenable assessment of cure level via ultrasonic reflection measurementsin a non-cure related signal variances independent calibrated responsemanner. Probe operation combined with appropriate instrumentationenables practical, reproducible and comparable measurement of the cureprocess and degree of cure for many cure sensing channels andquantitative comparison of the measurement values from test to test.

An ultrasonic waveguide sensor probe and testing system enablesdetecting materials cure and enables real time, in situ monitoring ofstructural material cure modulus change. The system operates bydistinguishing the propagation differences between various reflectionsignals modes of ultrasonic stress waves generated in the waveguideprobe and at waveguide structural material interfaces. A means,responsive to sensed acoustic signals, for distinguishing thedifferences between cure states of materials and temperature and processenvironment dependent factors and other non-cure related signalvariances that aid normalized ways for various waveguides and ultrasonicreflection test modes of ultrasonic stress waves so as to identify acure state of the material.

A differential ultrasonic waveguide cure monitoring probe in accordancewith various embodiments of the present invention may be designed toenable continuous, quantitative, temperature corrected in situ curemonitoring on many locations and with quantifiable cure level estimatesfrom different tests and different probes. Via analysis of thereflection signals, the cure probe can be extended to actual estimate ofthe cure material modulus.

The following describes several embodiments of the invention andexperimental measurements that were performed to demonstrate the utilityof the invention. To determine cure process of resin systems, ultrasonicmeasurements were performed using common polymers as a wave-guidematerial. Typical probe materials may include acrylic (PMMA),polystyrene, polyamide, or the like. The selection of ultrasonictransducers and/or wave-guide materials is dependent on expected resincure behavior, temperature requirements and desired sensitivity to theend cure condition. For example, for certain applications metals,ceramics, or glass may be used as the waveguide materials.

System

FIG. 1 is a schematic of an exemplary set-up for a short waveguideultrasonic reflection coefficient (URC) cure monitoring system showing adifferential ultrasonic waveguide cure monitoring probe 2 comprising awaveguide 3 and an ultrasonic transducer 4 (pulsar/receiver), a testsample of a material to be cured 6 in contact with a distal end of theprobe, and computer system 8 in communication with the ultrasonictransducer 4. As shown, the computer system includes a PC 8 incommunication with the differential ultrasonic waveguide cure monitoringprobe 2. The computer system 8 and probe 2 may communicate via hard wire(as shown) and/or wirelessly. The computer system is described in moredetail below, and may include a fully automated Ultrasonic ReflectionCoefficient (URC) system and associated electronics having multiplexing,signal gates, and supporting complete data collection and output. Forexample, the exemplary system may track ultrasonic signals from thesensor probe spanning automated signal intensity tracking range atbetter than 60 dB and continuous gated sampling of the signal over apredetermined period of time (e.g., minutes to many days).

The cure monitoring probe 2 arrangement may be suitable for automatedoperation for truly in situ mechanical monitoring of the cure processand involves no indirect interpretations of the signals, as is the casewith, for example, dielectric probe measurements. The differentialultrasonic waveguide cure monitoring probe 2 is preferably capable ofeconomical multiyear service, may be integrated into computerized cureprocess monitoring or/and may be retrofitted to existing materialsprocessing assemblies and operations.

FIGS. 2 and 3 illustrate typical ultrasonic interface reflectionparameters and define differential ultrasonic waveguide cure monitoringprobe key test measurement response. FIG. 2 shows an exemplarymeasurement set-up for the differential ultrasonic waveguide curemonitoring probe 2 based on short wave-guide probe, where R isreflection coefficient, Z is acoustical impedance, ρ is density and c isvelocity of sound. E_(I) represents the incident energy imparted to thewaveguide by the ultrasonic transducer, E_(R) represents the energyreflected by the probe/resin interface, and E_(T) represents thetransmission energy. Reflection coefficient R is defined via ration ofE_(R) and E_(I) or in terms of the difference of the Probe Z₁ and resinZ₂ impedances. FIG. 3 illustrates reflections at acoustical impedancelimits and shows the critical ultrasonic parameters governing signalinteractions at the probe-resin interface defining a relative reflectioncoefficient (R_(RRC)) value. Two factors govern the value of R_(RRC)measurements.

Reflection of the signal at the probe-resin interface 7 is function ofimpedance difference across the probe to resin interfaces. The value ofR can range from 0 to 1. Additionally, overall signal level of thereflection is function of the probe temperature, surrounding pressureand other environmental effects. The reference signals discussed laterundergo commensurate changes but are not influenced by resin properties.The probe reference signal relative changes provides additionalcorrection factor to create fully normalized and corrected values forthe R_(RRC) measurements. By knowing the impedance of the probe one cancalculate the impedance of a resin from the level of the signalreflection. The probe reflections can also be calibrated by reference tothe signal from the known impedance liquid. Thus, the differentialultrasonic cure monitoring probe signals can be interpretedquantitatively with respect to the measured cure condition and the finalstate of the resin cure.

The basic system (e.g., a transducer/waveguide, ultrasonic instrument,electronic instrumentation with means for signal storing and signalprocessing) can be adapted to different configurations by changing theset-up geometry, changing the transducer, and/or by changing waveguidetypes. By changing waveguide wave-front (i.e., the tip), frequency andreflection angle directivity, the stress waves ultrasonic tests may becontrolled and the apparatus may achieve enhanced performance to detectspecific types of cure conditions.

An exemplary application would be a waveguide cure tip set at criticalreflection angle at specified resin cure modulus. At the point the resinreaches the specified modulus, reflection signal level at the probe tipwould drastically change and essentially create a switching signal. Suchresponse can be used for a simplified cure monitoring process thatsenses the critical pre-set cure level of the resin.

Probe

Embodiments of the present invention provide in situ differentialultrasonic waveguide probes that enable real time monitoring ofmaterials' cure state. FIG. 4 shows an exemplary differential ultrasonicwaveguide cure monitoring probe 2 inclusive of ultrasonic transducer 4and attached waveguide sensing extension 3 that provides a soundreflection path for the “Interface Sensing,” used for cure monitoring,and a “Reference Signal,” for in situ continuous probe calibration. Alsoshown is a connection 9 for connecting the probe 2 to an ultrasonicinstrument, a computer system and/or electronics.

As shown, a reference structure 10 may be provided as part of thewaveguide 3 (see e.g., location A). A Reference Signal may be generatedby a transmitter of the transducer 4, travels through a first portion 3Aof the waveguide 3 to the reference 10, and then back to a receiver ofthe transducer 4. The Reference Signal may be used to compensate fornon-cure related signal variances including, for example,transducer/probe changes/effects due to overall operationalenvironmental effects, temperature changes, and/or pressure changes. AnInterface Signal may be generated sending a signal from a transmitter ofthe transducer through a first portion 3A and a second portion 3B of thewaveguide 3 to a probe tip 5 in contact with the curing material. TheInterface Signal then travels back from location B to a receiver of thetransducer.

As such, two ultrasonic signals are measured for the different probes(i.e., a Reference Signal and an Interface Signal). Reference Signalfrom location A is internal to the probe. The Interface Signal fromlocation B is generated at the probe tip, at the interface between probeand the matrix curing material. The amplitude of the signal reflectionat location A and location B may be analyzed to estimate cure level ofthe matrix. For example, the amplitudes of the reflections at location Bcorrected by reference signal changes at point A may be analyzed toestimate cure level of the matrix.

In operation, an ultrasonic pulse of selected frequency and pulse shape,originating at transducer 4, may be transmitted via the waveguide 3 tothe tip 5 of the probe 2 where a reflected signal is controlled by theimpedance properties of the waveguide to curing matrix couplinginterface 7. A portion of the initial pulse is reflected as a knownReference Signal from a reference feature 10 built in the sensingwaveguide 3. This reference feature 10 may incorporate acousticalreflectors that are part of waveguide such as, for example, across-section change, a slot incorporated in waveguide, a differentmaterial zone in the waveguide, or any suitable physical feature thatwill provide a known and stable ultrasonic reflector response.

The interface ultrasonic reflection signal is influenced by probeenvironmental materials response to temperature and/or pressure. Thesefactors can obscure the true signal response from the interface 7 to thecuring material. The Reference Signal is independently influenced bynon-cure related signal variances, such as temperature and pressure ofthe probe environment, and can be used to correct and recalibrate theprobe response at the cure sensing interface tip.

This correction/calibration enables non-cure related signal variances(e.g., temperature and/or pressure) independent measurement of the curestate (i.e., matrix modulus estimate) via sensor response that isuniformly calibrated and comparable for different tests with differentprobes and under different environments. There are many possiblewaveguide/transducer configurations that enable such measurements. Usinglinear amplifiers and digital signal capture of the ultrasonic signals,these measurements are readily converted to the physical data thatdirectly tracks cure progress and estimates the matrix modulus changedue to cure process.

Signal Response

FIG. 5 shows an exemplary initial, uncorrected signal response of theresin cure as sensed with the URC monitoring system of FIGS. 1-4 sensingthe R_(RRC) signal. As shown in FIG. 5, R_(RRC) signal response duringcure of, for example, polyester resin can be measured/monitored at roomtemperature and environment. Of interest in FIG. 5 is the large dynamicsignal range; constant and stable final R_(RRC) signal level; andsignificant signal changes during different initial cure stages. Thegraphs show all stages of the thermo-set cure process including gelatin,cure, transition stages, and the final cure level, as sensed by the curemonitoring probe. The horizontal axis represents time and the verticalaxis shows the relative signal from the probe.

The signal response signatures shown in FIGS. 6 and 7 are R_(RRC) curvesmeasured during the real time monitoring of the room temperature cureprocess for an exemplary fiberglass/polyester resin system. Signalresponse shown is typical data for the process widely used in boatbuilding or construction of large composite decks. The graphs show thethermo-set cure process including transition stages, and the final curelevel, as sensed by the cure monitoring probe. The horizontal axisrepresents time and the vertical axis shows the relative signal from theprobe.

One should note the large ultrasonic signal change and the dynamicsignal range plotted on the vertical axis that requires goodinstrumentation and low amplification noise. The polymer curecross-linking process is consistent with the response of this probeindicating stiffening of the resin with corresponding increase inacoustical impedance of the material. The R_(RRC) index response iscontrolled by resin mechanical properties and is related to the changein resin density and elastic constants. Such ultrasonic measurementsdirectly sense mechanical condition of the resin and can predict themechanical condition of the material. The resin cure process generatesspecific mechanical changes that are identifiable in the sensor responseand can be monitored for process verification and control. The sensoronly requires one side access and does not depend on distance or timemeasurements employed by many other conventional ultrasonic curemonitoring methods.

The example of FIG. 6 shows the relative reflection coefficient(R_(RRC)) versus time for the proper cure of the fiberglass/polystyreneresin composite during process indicating stages of the cure cycle. Asshown in FIG. 6, a R_(RRC) signal shape from a good cure process wherethe signal reaches a low level threshold and stabilizes at constantvalue indicating completion of the cure process.

FIG. 7 illustrates insufficient cure as sensed by response of theR_(RRC) signal from the cure sensor in a fiberglass/polystyrene resincomposite during a cure process indicating insufficient solidificationof the material being cured. As shown in the example of FIG. 7, aR_(RRC) signal from an inadequate cure process where resin never reachesdesired cure state and the cure process after more than 41 hours has notstabilized. The incomplete cure process could be due to possibleimproper resin formulation, over-aged resin components, low environmenttemperature or externally contaminated resin. Regardless of the impropercure origin, the R_(RRC) value indicates lack of resin mechanical andchemical consolidation and positively records insufficient materialprocessing conditions.

A basic differential ultrasonic waveguide cure monitoring probe testconfiguration, such as shown in FIGS. 1-3 and with probe configurationas shown in FIG. 4, enables direct and reproducible measurements of themechanical cure state of the resin material. Because impedance of theresin is a product of the density and sound velocity of the resinmaterial, the interface B reflection is a function of the resinimpedance change due to cure process. As the resin cures, the resinultrasonic velocity changes proportionally to the resin mechanicalmodulus change. As a result, the reflection coefficient at interface Bis affected and represents the modulus change of the curing resin.Temperature, pressure and environmental factors (collectively non-curerelated signal variances) can modify reflection values at interfacelocation B of the waveguide probe and resin system. These same factorsor non-cure related signal variances affect signals at the interfacelocation A that is built in as a reference reflection signal in thewaveguide probe. The signal reflections at location A that areindependent of the resin are used to correct, and normalize responsesignals from location B, thus creating stable and reproduciblereflection coefficient measurements of the resin at location B, andminimizing effects of environmental factors. Such differentialarrangement with initial system normalization calibration enables thereflection measurements at location B to be directly correlated to theactual mechanical modulus of the resin.

A single probe with supporting ultrasonic data acquisition system can beused at any desired location in the composite curing arrangement tomonitor a local cure process by continuous recording of the reflectionsignal from interface locations B and A. In some embodiments, thefrequency of the test may generally be between 1 and 10 MHz, and theseparameters may be adjusted for the specific cure material and waveguiderequirements. For example, larger structures with thicker parts will ingeneral use lower frequencies and proportionally larger probes. Forgeneral applications, ultrasonic transducers with 5, 10 and/or 15 MHztest frequencies using nominally ¼ inch to ⅛ inch diameter waveguide,are practical and flexible to sense cure of most thermo-set materials.

Other Probe Configurations

FIGS. 8A-8E show several exemplary probe/sensor embodiments withtemperature reference standards for improved differential ultrasoniccure monitoring. As shown in FIGS. 8A-8E respectively, the probe mayinclude: a cross-section reference probe; an insert reference probe; anedge reference probe; an insert/void reference probe; a notch referenceprobe; and the like. Each embodiment of the differential waveguide curemonitoring probe includes a transducer operatively coupled to awaveguide attachment and a reference incorporated into or formed as partof the waveguide. The shape of the waveguide may vary depending on theapplication. For example, the waveguide probe may be round or faceted asper application function.

FIGS. 9A-9D show different views and further details of an exemplarycross-section reference differential probe 2 for the hard mount in thetooling surfaces. FIG. 9A shows a perspective view of the cross-sectionreference probe having an ultrasonic transducer 4 connected to awaveguide body 3. FIG. 9B shows a cross-sectional view of the probe ofFIG. 9A and one suitable manner of connecting the ultrasonic transducer4 and the waveguide body 3. FIG. 9C shows a tip 5 detail and FIG. 9Dshows an exemplary surface treatment and triangular lip 12 located onthe circumference of the probe tip 5. As shown, the lip 12 may belocated intermittingly (e.g., 80 degree sectors) around the tipcircumference with gaps 13 (e.g., 40 degrees) in between the lipsectors. The tip may include a surface treatment 14. Surface treatmentsmay include cleaning, etching and possible coating of the probe tip toenhance coupling and adhesion of the probe to the resin material.Surface treatments may vary for different probe materials and may be assimple as solvent wipe and controlled micro-roughness of the tipsurface, for example.

As shown, the waveguide 3 has a first portion 3A having a firstcross-section and a second portion 3B having a second cross-section. Inthe illustrated embodiment, the first portion 3A has a largercross-section than the second portion 3B. The first portion 3A may beused to measure the reference signal, and the first and second portions3A, 3B may be used for interface sensing. The probe 2 may include directmount threads (e.g., 5/16-32 thread) for threaded engagement withcorresponding tooling side hole/threads. A probe seal may be providedand may be customized for the specific application, using for example;O-rings, paste, via Teflon tape or similar sealing techniques. This typeof probe may be mounted to modified delay line transducer housingsdirectly or via a coupling ring.

FIGS. 10A-10E show different views and further details of an exemplaryslot reference differential probe 2 for the hard mount in the toolingsurfaces. FIG. 10A shows a perspective view of the slot reference probe2 having an ultrasonic transducer 4 connected to a waveguide body 3 witha slot reference 10. FIG. 10B shows a cross-sectional view of the probeof FIG. 10A and a threaded connection between the ultrasonic transducer4 and the waveguide body 3. FIG. 10C shows a tip 5 detail, and FIG. 10Dshows an exemplary surface treatment and triangular lip 12 located onthe circumference of the probe tip 5.

As shown, the waveguide 3 has a first portion 3A from the connectionbetween the ultrasonic transducer 4 and waveguide body 3 and extendingto the slot 10 and a second portion 3B extending from the slot 10 to theprobe tip 5. The first portion 3A may be used to measure the referencesignal and the first and second portions 3A, 3B in combination may beused for interface sensing. The probe 2 may include direct mount threads(e.g., 5/16-32 thread) for engaging corresponding threads in a hole inthe tooling side. A probe seal may be provided and may be customized forthe specific application, using for example: O-rings, paste, via Teflontape or similar sealing techniques. This type of probe may be mounted toa modified delay line transducer housing directly or via a coupling ringadapter.

FIGS. 11A-11D show different views and further details of an exemplarysmall transducer cross-section reference differential probe 2 for thehard mount in the tooling surfaces. FIG. 11A shows a perspective view ofthe miniature screw on cure monitoring probe 2 having a cross-sectionreference 10. FIG. 11B shows a cross-sectional view of the probe 2 ofFIG. 11A and a threaded region wherein the ultrasonic transducer 4 mayscrew into a hole having corresponding threads in the proximal end ofthe waveguide body 3. FIG. 11C shows a tip 5 detail at the distal end ofthe waveguide 3, and FIG. 11D shows an exemplary surface treatment andtriangular lip 12 located on the circumference of the probe tip 5.

FIGS. 12A-12D show different views and further details of an exemplarycross-section reference differential probe 2 having a collar coupling22. As shown, a coupling ring 22 may be used to connect the transducer 4and the waveguide 3.

FIG. 13 shows an alternate embodiment of the probe 2 having a shaped(e.g., non-linear) waveguide design. For example, the waveguide mayinclude a curved body having a radius or an angled body having cornersappropriate to guiding ultrasonic waves to a location per applicationfunction. As shown, the waveguide includes a first portion 3A and asecond portion 3B. The second portion 3B includes a third portion 3C, afourth portion 3D, and a corner 20 for redirecting the signal betweenthe third portion 3C and fourth portion 3D. In special designs, thewaveguide can be made integral to the composite parts-tooling or thewaveguide probe can integrate tooling material or tooling surfaces as anextension to the ultrasonic path of the waveguide.

The probe sensing interface tip 5 can be geometrically modified for theoptimum test coupling such as shown for the composite pre-preg curemonitoring where the tip 5 incorporates fiber stand off ridges or lips12. Additionally, probe waveguide material may be selected for bestresponse to cure changes in the matrix and probe sensing interface maybe modified to optimize coupling to the matrix material and the probe.Interface modifications can include surface treatment 14 such as, forexample, solvent etch of the surfaces or separate coating of theinterface surfaces for optimum vetting and coupling to the resin matrix.

The dimensions shown in FIGS. 9A-13 are exemplary and may vary fordifferent application needs. For example, the probe lengths may be aboutone inch to in excess of 12 inch.

The probes can be designed around standard delay line transducerhousings as shown in FIGS. 14A-14C. As shown in the various figures, aprobe and transducer may be connected/coupled together using a varietyof techniques, such as screwing the two pieces together.

Multi-Probe and Automation

FIG. 15 shows a multi-probe set-up and some of the system hardware andelectronics. As shown in FIG. 15, the system hardware may including anA/D board 30, an ultrasonic pulser/receiver card, and a channelmultiplexer board. One or more differential ultrasonic waveguide curemonitoring probes (e.g., transducer 1 and transducer 2) may be coupledto the system hardware and electronics via wire or wireless means. TheMUX board may be used to switch between two different transducers. Byanalog amplification, gating, digital signal capture, signal processingand digital data analysis and processing, such cure testing/monitoringcan be performed totally automated.

The system work as follows:

1) Get calibration signals on transducers.

As shown in FIG. 15, two transducers may be put on the system, one foreach channel. On each channel, two numbers may be gathered: the peakamplitude of the signal when the transducer is in air, and the peakamplitude of the signal in a second medium. These numbers should bestored in the file when the data files are created (see step 5 below).For a two probe embodiment, there will be two sets of these peakamplitudes gathered—one for each channel.

2) Set the transducers in the resin to be cured (hardened). Preferably,no software interaction is needed.

3) Set gates.

Gates should be positioned over the signal to be checked. Preferably,there will be at least one gate on the signal. Note that there may betwo settings for this gate: one when switched to channel 1, and one whenswitched to channel 2.

4) Set the recording rate and time to record.

Set how often and how long to collect data. In the illustratedembodiment, data may be collected on channel 1 and channel 2, so thesystem may switch from channel 1 to channel 2 using the multiplexingfunction. Preferably, at a low end about 40 to about 100 tests a secondare tried, and at a high end a test every minute or so. There shouldalso be a time limit on how long to record data (e.g., 3 minutes, 3hours, 3 days, etc.)

An ultrasonic transducer, or even remote laser acoustical source, may beused to generate controlled frequency and wave-front ultrasound signalin a waveguide including bulk, shear, and/or other guided mode acousticwaves. Alternatively, a laser light may be delivered to a waveguidesurface through mirrors, fiber optic bundles, light pipes orcombinations of optical components. FIG. 4 illustrates schematically thearrangement of the elements of an exemplary embodiment of a differentialultrasonic waveguide cure monitoring probe for forming and controllingultrasonic tests.

The same ultrasonic transducers, or another ultrasonic transducer, orpossibly a remote non-contact receiver on the waveguide termination maybe used for sensing to help in redirecting the reflected sound fieldsfrom the reference and waveguide/resin interface location. Waveguidesenable capture of the signal at different angles from multiple locationsand allow the receiving transducers to be laced at more flexiblelocations. Arrays of waveguides enable capture of ultrasonic signalsfrom different sources.

5) Start recording.

A button or remote signal should start recording data. At everycollection, the peak amplitudes should be gathered and stored in a file.The option to pause the collection and resume it later may be provided.Data will not be written to the file while the system is paused. Also,there should be a graph of the amplitude data displayed over time (e.g.,either linearly or on a log scale).

6) Stop recording.

Recording will stop after the time limit is reached or when it iscancelled by the user.

Data may be collected with a data capture and storage unit, whereuponthe data may be processed and decisions may be made with regard to thedegree of cure or materials modulus change. Embodiments of the presentinvention enable one to generate and detect ultrasonic signals from asingle location using one waveguide probe coupled ultrasonic transducer.The methodology enables one to control the wave front, frequency, andreflection parameters of the acoustic signal for optimum interactionwith the material and detection of the cure process affected ultrasonicinterface echoes.

Measurements Concept

The following paragraphs expand the measurements concept of the presentinvention by providing a specific description of an exemplarymeasurement process that enables calibrate and quantitative sensing ofthe cure level in the polymeric materials and composites (i.e., thematerial to be cured). As described, embodiments of the differentialcure monitoring approach extends the measurements of the cure todifferential non-cure related signal variances (e.g., temperature)compensating waveguide arrangements. The differential temperaturemeasurements enable practical reproducibility of signals measurementsand calibration of the absolute value of the cure levels. Calibration ofcure level/degree enables quantitative assessment of the mechanicalcondition of the polymer resin/composite material, and thus, asignificant improvement over current state of the art methodologies thatcannot directly and in situ determine actual cure state of the material.

The ultrasonic signals are typical examples of RF or rectified UT echoesthat will be gated by a cure signal capture processor. There are severalsteps to achieve and measure the calibrated reference reflection signal(R_(RRC)).

First, the amplitude of the main end point waveguide reflection ismeasured in air or from a controlled impedance liquid at a determinedtemperature. For example, room temperature around 25 degrees C. Thenormalized R_(RRC) reflection is defined and calibrated as 1 by dividingthe controlled impedance reflection amplitude measurement by itself forall the channels and transducers.

Thus, regardless of the set-up to set-up and test to test variability ofthe transducers, waveguides, amplifiers, cables and/or electronics, thecure monitoring sensor initial signal levels are synchronized (e.g., ata value of 1) and comparable to each other. This process assumeslinearity of the electronic-transducer system and similar sensingresponse over the reflection interfaces during the cure processingtests. System linearity is a reasonable assumption with modernelectronics customized for these types of measurements.

The R_(RRC) reflection coefficient retains the reference normalizationby dividing the reference echo numeric measurement of signal amplitudewith the new values of the resin-probe interface signal amplitude—thatis by continuous correcting resin-probe interface signal amplitude(Point B) by the changes in the probe internal reference signalmeasurements (point A), as illustrated in FIG. 4. This procedure assumeslinear ultrasonic dynamic range and minimum dispersion effects due tosome fundamental frequency variances between the probes. This correctionprocedure also accounts for and minimizes the variance in individualpulse signal amplitudes due to electronic channel, transducer-proberesponse, cable and other amplitude affecting differences/variants.

If there were no temperature effects, this calibration itself allowsmore reproducible measurements of the ρc changes at the probe-resininterface. However, most of the resins exhibit some exothermic heating,temperature is not constant during long cure process, or the cureprocess is performed in ovens and autoclaves that operate at elevatedtemperatures and pressure.

Thus, the relative reflection coefficient signal R_(RRC) has to befurther corrected by differential reference echo signal that compensatesfor the temperature effect on the probe (as well as other non-curerelated signal variances). One simple way is to utilize and monitoradditional echo in each probe that is only affected by temperature andis independent of the resin signal.

This temperature reference signal measurement can be achieved by probedesign incorporation signal interface reflectors (i.e., a reference aspart of the waveguide) that are dominantly influenced by temperature (orpressure or environmental) effects. As shown in FIGS. 8A-13, forexample, there may be a wide range of the possible probe configurationsthat enable this additional correction.

Overall, the simplest calibration algorithm for R_(RRC) is:

R _(RRC) =E _(R) /E _(Air)×1/(E _(RTemp) /E _(RRef Temp)

where:

-   -   R_(RRC)=Relative Reflection Coefficient    -   E_(R)=Reflected Amplitude at probe resin interface    -   E_(Air)=Reflected Amplitude probe “air” interface    -   E_(RTemp)=Reflected Amplitude from temperature interface    -   E_(RRef Temp)=Reflected Amplitude from temperature interface at        selected calibration temperature (usually same as E_(Air)        measurements)

The measurements of the amplitude can be performed by peak signaldetection of the RF ultrasonic signal or peak detection of the rectifiedand filtered ultrasonic RF signal. In advanced applications with noiseproblem, the detection can include signal processing such as frequencyanalysis of the ultrasonic echoes and amplitude (energy) measurement atthe selected frequency domain.

Ultrasonic R_(RRC) values may be collected as a function of time andother process parameter, such as temperature. As such, it is possible todevelop typical cure process reference curves from, for example, labcontrolled resin cure response tests and the development testmeasurements on actual part configurations. Ultrasonic R_(RRC) responsecurves may be presented as a function of time and/or processmanufacturing steps. These RRC response curves are characteristic of theprocess and may serve as control and acceptance for the anticipate acure response.

FIGS. 16-20 show anticipated signal waveforms capture for an exemplary2.25 MHz transducer signal using standard impulse driven ultrasonic testinstrument.

FIG. 16 shows an exemplary gated ultrasonic signal showing initialpulse, temperature reference echo and cure interface echo. Signals arefor the PMAA 1⅜ inch probe with a reference slot at ⅞ inch (see e.g.,FIGS. 10A-10D).

Exemplary reference and interface RF signals for the 2.25 MHz guidedwave probe with a reference slot reflector is shown in FIG. 17. Thereference signal is from an exemplary ⅓ cut/slot in the 2 inch longwaveguide probe. As shown in FIGS. 16-17, the signal gating options mayinclude,

-   -   Full rectified and filtered signal as in FIG. 16. Peak        detection.    -   Unprocessed RF signal peak amplitude detection, as in FIG. 17.    -   +RF signal peak detection.    -   −RF signal peak detection.

FIG. 18 shows a digitally captured and plotted waveguide ultrasonic RFsignal in an exemplary 2 inch PMAA probe (¼ inch diameter) with driveand sensing interface reflected air calibration signal.

FIG. 19 shows an exemplary ultrasonic record of the 2.25 MHz signal withslot reference for an exemplary 1.389 inch PMMA having a reference cutat about 0.494 inch. For nominally 100 V transducer drive pulse at 0.5us half-width, a typical voltage of the signal return for a cured resinis expected in the 50 mV to 5 μV. Thus a receiver should be able toresolve around 80 dB signal range or have auto-gain control.

FIG. 20 is a flowchart showing an exemplary process for differentialultrasonic waveguide cure monitoring. As shown in FIG. 20, the processmay begin with the user initiating the computer system and electronicsStep 200. A display 210 showing an exemplary initial set-up screen isillustrated in FIG. 22. At step 220, the user selects a program to run.The programs may include, for example, a new set-up (step 212), a savedprogram (step 213), and a data analysis (step 214).

As shown in FIG. 20, at step 215 a new set-up program (212) may displaya UT screen that allows the user to perform/select one or more functionsincluding, for example, channel definition, transducer calibration,gates setting, data settings (e.g., sample data rate, gain, log/linear,etc.), file record settings, and the like. Once the new set-up iscomplete, the user may save it or go to test (step 220). At step 225,the cure monitoring process may proceed with a test run screen with datadisplay and settings display, a UT signal display, start and stopbuttons, external trigger or control inputs, alarms (e.g., gate out, nosignal, low signal, high signal, etc.). At step 230, the processcontinues and data file storage may occur.

If a saved program (213) is selected at step 220, the process continuesto step 235 and a saved program may display a UT screen, transducercalibration, gates check, file record setting, and the like. The processmay then proceed to step 225 and step 230 (described above). If a dataanalysis program (214) is selected at step 220, the process continues tostep 240 and one or more of the following functions may be performed:file load and review, scroll, plot, channel compare, calibration review,calibration scale factors analysis, Export (ANSI, Excel, etc.). Theprocess may also access the data file storage at step 230.

FIG. 21 shows an exemplary test set-up including a differentialultrasonic waveguide cure monitoring probe in contact with a resinmaterial to be cured and connected to a computer having a processing anddigital data storage capacity. Display 210 may be part of the computer 8and may display information regarding the cure process and level of cureto the user. For example, as shown in FIG. 22 the display 210 mayinclude information relating to set channel switch rate, zooming,panning, channel n graph/scope (gate n) display, channel n selection,start, exit, data normalization, gate control, signal marking/tracking,data recording, graph/scope control, file control, and the like.

As noted from FIGS. 20-22, for example, convenience features such as setup recording, graphic presentations or memory access to previous data,may be included in computer monitoring applications. As in all moderncomputer system, data interchange and interface to other devices, suchas process controllers and/or alarms notices, may be provided forintegrated manufacturing controls.

Further, a single channel ultrasonic instrument can be extended viaelectronic and computer multiplexing to any number (n) of channels. Thismay enable cure monitoring in larger composite processing operations.Depending on the manufacturing needs, individual probes can be locatedon strategic component locations to locally assess cure process at, forexample, the different zones of the parts. This multi-site monitoringmay be desirable for products with possible part thickness variance,resin infusion delays, local thermal conditions or a host of otherprocessing needs. In multi-channel operation, each probe data maybeindividually recorded, and the probes information may be processed inidentical manner as a single probe test procedure.

In multi probe configurations, test data from probes may be compared toestablished baseline cure data. By comparison of different probesresponses, it is possible to make informed engineering decisions on thecure process. The data capture and processing aspect of the presentinvention may include signal analog amplification, signal gating, andsignal capture by digital means with multi-channel capability atresolutions as needed to process the signals. Ultrasonic signals may begated and analyzed in the time and frequency domains, classified viaanalysis or other feature and classification algorithms. Dedicatedprocessors and software may be used to automatically characterize orassist in characterization of signal changes that track the differentialultrasonic waveguide cure monitoring probe response.

Computer

FIG. 23 depicts an example computing environment 100 (e.g., the computersystem or PC shown in FIGS. 1 and 21) in which an example embodiment maybe implemented. Computing environment 100 may include computer 110,monitor 191 and other input or output devices such as mouse 161,keyboard 162 and modem 172. Computers and computing environments, suchas computer 110 and computing environment 100, are known to thoseskilled in the art and thus are briefly described here.

An example system for implementing an embodiment includes a generalpurpose computing device in the form of computer 110. Components ofcomputer 110 may include central processing unit 120, system memory 130and system bus 121 that couples various system components including thesystem memory to processing unit 120.

System memory 130 may include computer storage media in the form ofvolatile and/or nonvolatile memory such as ROM 131 and RAM 132. A basicinput/output system 133 (BIOS) containing the basic routines that helpto transfer information between elements within computer 110, such asduring start-up, may be stored in ROM 131. RAM 132 typically containsdata and/or program modules that are immediately accessible to and/orpresently being operated on by central processing unit 120. Systemmemory 130 additionally may include, for example, operating system 134,application programs 135, other program modules 136 and program data137.

Embodiments may be implemented in computing environment 100 in the formof any of a variety of computer readable media. Computer readable mediacan be any media that can be accessed by computer 110, including bothvolatile and nonvolatile, removable and non-removable media.

Computer 110 may operate in a networked environment using logicalconnections to one or more remote computers, such as remote computer180. Remote computer 180 may be a personal computer, a server, a router,a network PC, a peer device or other common network node, and typicallyincludes many or all of the elements described above relative tocomputer 110. The logical connections depicted in FIG. 1 include localarea network (LAN) 171 and wide area network (WAN) 173, but may alsoinclude other networks. Such networking environments may be common inoffices, enterprise-wide computer networks, intranets, and the Internet.

When used in a LAN networking environment, computer 110 may be connectedto LAN 171 through network interface 170. When used in a WAN 173networking environment, computer 110 may include modem 172 forestablishing communications over WAN 173, such as the Internet. Modem172 may be connected to system bus 121 via user input interface 160, orother appropriate mechanism.

Computer 110 or other client device can be deployed as part of acomputer network. In this regard, various embodiments pertain to anycomputer system having any number of memory or storage units, and anynumber of applications and processes occurring across any number ofstorage units or volumes. An embodiment may apply to an environment withserver computers and client computers deployed in a network environment,having remote or local storage. An embodiment may also apply to astandalone computing device, having programming language functionality,interpretation and execution capabilities.

Tooling Mounting Options

In some embodiments, the waveguide can be made integral to the compositeparts-tooling, or the waveguide probe can integrate tooling material ortooling surfaces as an extension to the ultrasonic path. FIGS. 24-26show several embodiments having tooling mounting options. As shown inFIG. 24, a silicone rubber skirt or equivalent may be provided proximatethe distal end of the probe to enable mounting of the probe on a vacuumbag side. As shown, the probe waveguide may extend through a hole oropening in the skirt and the tip or front face of the probe may contactthe material being cured. In another embodiment, the tool mount mayinclude hard tooling, such as shown in FIGS. 25 and 26. The hard toolingmay be in contact with the materials being cured and may be used as ameans of ultrasonic coupling of the waveguide probe to the compositematerial. As shown, a seal, for example an o-ring seal, may be providedbetween the probe waveguide extension and the tooling.

Critical Angle Reflection Probes

FIGS. 27-29 show several probe embodiments having critical anglereflection geometries at the probe tip. As shown in FIG. 27, anexemplary critical angle reflection probe may include a tip geometryhaving multiple angled structures. The shape and angle of the probe tipmay be selected based on the particular application and the desiredcritical angle. Also shown is the sound path reflection at the selectedcritical angle. FIG. 28 shows a probe having a single tip angle forproducing the desired sound path via reflection for the tip angle. FIG.29 shows a multi-surface reflection geometry waveguide termination incontact with a composite material.

Definitions

Curing is a term in polymer chemistry and process engineering thatrefers to the toughening or hardening of a polymer material bycross-linking of polymer chains, typically brought about by chemicaladditives, ultraviolet radiation, electron beam or heat. The curingprocess transforms the resin into a plastic or rubber by a cross-linkingprocess. Despite the wide variety of thermo-set resin formulations(epoxy, vinylester, polyester, etc.), their cure behavior isqualitatively identical. The resin viscosity drops initially upon theapplication of heat, passes through a region of maximum flow and beginsto increase as the chemical reactions increase the average length andthe degree of cross-linking between the constituent oligomers. Thisprocess continues until a continuous 3-dimensional structure is created.Cure monitoring methods give a significant insight to the chemicalprocess and define process actions towards achieving specific qualityindices of the cured resin systems.

Real-time computing of cure monitoring is an essential component for thecontrol of the manufacturing process of composite materials. Therationale for cure monitoring relies on the various physical and/orchemical properties that can be used to follow the transformation of aninitially liquid thermo-set resin into its final rigid solid form(curing).

Cure material includes thermosetting plastics (thermo-sets) and polymermaterials that irreversibly cure. Examples of materials that may be cureinclude, but are not limited to: polymers; polymer composites; polyesterfiberglass systems; fiber reinforced composite materials; vulcanizedrubber; resins; polymeric resins; phenol-formaldehyde resin;urea-formaldehyde foam; melamine resin; epoxy resin; polyamides; and thelike.

A waveguide is a device or structure designed to confine and direct thepropagation of waves (i.e., that guides waves), such as sound or lightwaves. An acoustical waveguide is a physical structure for guiding soundwaves.

An ultrasonic transducer is a device that generates and sends highfrequency sound waves. An ultrasonic transducer may also receive backthe echo of the high frequency sound waves. An example of an ultrasonictransducer is a piezoelectric transducer that converts electrical energyinto sound waves. Upon receipt of the echo, the ultrasonic transducerturns the sound wave into electrical energy which can be measured. Anultrasonic transducer may generate sound waves above about 20,000 Hz.The transmitter and receiver components may comprise separate devices ormay be combined in a single device. One use for ultrasonic transducersis non-destructive testing.

Non-cure related signal variances are effects caused by one or more of:temperature effects, pressure effects, humidity effects, variances intransducer response, variances in waveguide response, variances inoverall probe response, variances in instrument and signal channelresponse, and the like. Non-cure related signal variances may becompensated for or corrected using the differential ultrasonic waveguidecure monitoring probe and the independent calibrated response manner.

The differential ultrasonic waveguide cure monitoring probe has beendemonstrated to be very sensitive to different stages of a cure cycleand appears to be effective in quantitative determination of the finalcure. The benefits of this configuration are based on the simplicity ofthe probe, low cost of the wave-guide, ability to quantitativelycalibrate the signals and ability to configure the probe to a variety ofresins and processes. The ultrasonic waves are very sensitive to theinterface impedance changes and the differential ultrasonic waveguidecure monitoring probe (UCS) is adapted to utilize and maximize thisphenomenon.

Overall, the UCS probe approach with R_(RRC) signal sensing has manyapplication advantages/benefits including:

-   -   The probe design is very inexpensive.    -   All transducers, cables and instrumentation are reusable.    -   The sensor system can be calibrated and is suitable for final        cure tracking.    -   Ultrasonic resin cure determination is a more direct measure of        the mechanical state of a resin than other types of cure        sensors.    -   The sensor design is adaptable to modern ultrasonic        instrumentation that can multiplex signals and support many        channels.    -   Sensor fundamental design has robustness and is adaptable for        wide range of resin types by modifications and customization of        the probe ρc properties.    -   The probe design enables absolute calibration on ultrasonic        signal amplitude.    -   The probe design further enables the measurement of the        differential temperature effects allowing for the correction of        the signal amplitude changes due to temperature.    -   Integrating probe response with signal capture and processing        functions enables quantitative multi-sensor cure response        comparison.

While the present invention has been described in connection with theexemplary embodiments of the various Figures, it is not limited theretoand it is to be understood that other similar embodiments may be used ormodifications and additions may be made to the described embodiments forperforming the same function of the present invention without deviatingtherefrom. Therefore, the present invention should not be limited to anysingle embodiment, but rather should be construed in breadth and scopein accordance with the appended claims. Also, the appended claims shouldbe construed to include other variants and embodiments of the invention,which may be made by those skilled in the art without departing from thetrue spirit and scope of the present invention.

What is claimed:
 1. A differential ultrasonic waveguide cure monitoringprobe for in situ ultrasonic monitoring of a material undergoing a cureprocess, the probe comprising: an ultrasonic transducer; a waveguidehaving a proximal end in contact with the ultrasonic transducer and adistal end for contacting the material undergoing the cure process, thewaveguide comprising: a first portion extending from the proximal end; areference of the waveguide; a second portion extending from thereference to a tip at the distal end of the waveguide; an ultrasonicsignal generated by the ultrasonic transducer and transmitted into thewaveguide; an interface signal generated by a portion of the ultrasonicsignal reflecting back from the interface of the probe and the materialundergoing a cure, the interface signal reflecting back to theultrasonic transducer, the interface signal being used to directly sensethe mechanical modulus change of the curing material; and a referencesignal generated by a portion of the ultrasonic signal reflecting backfrom the reference, the reference signal reflecting back to theultrasonic transducer, the reference signal being used to recalibratethe probe and account for non-cure related signal variances during thecure process; wherein a quantitative assessment of a cure level of thematerial undergoing the cure process is determined in a non-cure relatedsignal variances independent calibrated response manner using thereference signal to correct/recalibrate the interface signal.
 2. Thedifferential ultrasonic waveguide cure monitoring probe of claim 1,wherein the response signal is internal to the probe and independentlyinfluenced by the probe environment and can be used to continuouslycorrect and recalibrate the probe response as measured by the interfacesignal, which measures changes in signal reflection/transmission due toimpedance change in the curing material.
 3. The differential ultrasonicwaveguide cure monitoring probe of claim 1, wherein the waveguidereference further comprises a cross-section reference, thecross-sectional reference comprising: a first portion having an firstcross-sectional area; and a second portion having a secondcross-sectional area, the second cross-sectional area being smaller thatthe first cross-sectional area; wherein the reference is the portion ofthe first cross-sectional area that extends beyond the secondcross-sectional area.
 4. The differential ultrasonic waveguide curemonitoring probe of claim 1, wherein the waveguide reference furthercomprises a slot reference, the slot reference comprising a slot in thewaveguide extending from a side of the waveguide toward a center of thewaveguide and substantially orthogonal to a longitudinal centerline ofthe waveguide.
 5. The differential ultrasonic waveguide cure monitoringprobe of claim 1, wherein the waveguide reference further comprises asmall transducer cross-section reference.
 6. The differential ultrasonicwaveguide cure monitoring probe of claim 1, wherein the waveguidereference further comprises an insert/void reference.
 7. Thedifferential ultrasonic waveguide cure monitoring probe of claim 1,wherein the waveguide further comprises an alternate geometry, thealternate geometry comprising an angled body wherein the second portionof the waveguide extends at an angle relative to the first portion ofthe waveguide.
 8. The differential ultrasonic waveguide cure monitoringprobe of claim 1, wherein the probe is in direct contact with thematerial undergoing the cure process, the probe is only connected to oneside of the material being cured, and the cure monitoring is performedin situ to allow real time monitoring of the cure process.
 9. Thedifferential ultrasonic waveguide cure monitoring probe of claim 1,wherein the probe is initially calibrated before the cure process usinga material having known characteristics and wherein the probe iscontinuously calibrated during the cure process using the referencesignal to account for non-cure related signal variances during the cureprocess in order to provide quantitative assessment and comparison ofcure rates and degree of cure completion.
 10. The differentialultrasonic waveguide cure monitoring probe of claim 1, wherein thematerial being cured comprises any thermo-setting material.
 11. Thedifferential ultrasonic waveguide cure monitoring probe of claim 1,further comprising a front face located at the tip, the front surfacesuitable for direct contact with the cure material and for ensuringcoupling of the ultrasonic signal across the probe/material interface.12. The differential ultrasonic waveguide cure monitoring probe of claim11, wherein the tip and front face further comprise a critical anglereflection structure.
 13. The differential ultrasonic waveguide curemonitoring probe of claim 12, wherein the critical angle reflectionstructure further comprises multiple surface refection geometrywaveguide terminations.
 14. The differential ultrasonic waveguide curemonitoring probe of claim 1, wherein the tip further comprises a liplocated on the circumference of the tip.
 15. An in situ method formonitoring the cure of a curable material comprising: calibrating theprobe by reference to the final from a material having a knownimpedance; coupling a differential ultrasonic waveguide cure monitoringprobe to a material to be cured, the differential ultrasonic waveguidecure monitoring probe comprising an ultrasonic transducer and awaveguide extending from the ultrasonic transducer; positioning theprobe with a tip and front face of the waveguide in direct contact withthe material to be cured; directing a pulse of ultrasound energy throughthe waveguide toward the material being cured, wherein a portion of theultrasound energy is reflected back from the reference structure of thewaveguide, and a portion of the ultrasound energy is reflected back froma materials boundary interface between the probe and the material beingcured; sensing the ultrasound energy reflected from the materialsboundary interface between the probe and the material being cured;sensing the ultrasound energy reflected from the reference; correctingthe sensed ultrasound energy reflected from the materials boundaryinterface using the sensed ultrasound energy reflected from thereference; and determining a real time measurement of the modulus of thematerial being cured at a particular point in the curing process usingthe sensed ultrasound energy reflected from the materials boundaryinterface and from the reference.
 16. The method of claim 15, whereinthe step of sensing the ultrasound energy reflected from the materialsboundary interface further comprises: analyzing the amplitude of thereflected ultrasound energy from the materials boundary interface andthe reference; periodically analyzing the amplitude of the waveform ofthe reflected ultrasound energy from the materials boundary interface todetermine whether the modulus of the composite has reached apredetermined modulus; and terminating the cure process once thepredetermined modulus is reached.
 17. The method of claim 15, whereinthe step of correcting the measurement further comprises continuous insitu temperature compensation of the ultrasound energy reflected fromthe materials boundary interface using the ultrasound energy reflectedfrom the reference to ensure accurate and reproducible sensing of thecure material during the cure process.
 18. The method of claim 15,wherein the step of correcting the measurement further comprisescontinuous in situ non-cure related signal variances recalibration ofthe ultrasound energy reflected from the materials boundary interfaceusing the ultrasound energy reflected from the reference to ensureaccurate and reproducible sensing of the cure material during the cureprocess.
 19. The method of claim 15, wherein a series of pulses ofultrasound energy, and corresponding reflected reference signals andreflected interface signals, are generated and sensed over a period oftime at predetermined time intervals.
 20. A method for detectingmaterial cure comprising: performing an initial signal calibration of aprobe comprising an ultrasonic transducer and a waveguide; coupling thewaveguide of the probe to the material to be cured; generating anultrasonic stress wave in a waveguide using the ultrasonic transducer;generating a response signal by reflecting a portion of the generatedultrasonic stress wave from a reference of the waveguide back to theultrasonic transducer; generating an interface signal by reflecting aportion of the generated ultrasonic stress wave from an interface of thewaveguide and the cure material back to the ultrasonic transducer;performing non-cure related signal variances correction/compensation ofthe sensed interface signal using the sensed reference signal; anddetermining a quantitative degree of cure of the materials using thecorrected signal.
 21. A method for detecting material cure comprising:coupling the waveguide of the probe to the material to be cured;generating an ultrasonic signal in the waveguide using the ultrasonictransducer; generating a response signal that is independent of the curematerial by reflecting a portion of the generated ultrasonic signal froma reference of the waveguide back to the ultrasonic transducer;generating an interface signal by reflecting a portion of the generatedultrasonic signal from an interface of the waveguide and the curematerial back to the ultrasonic transducer; distinguishing thepropagation differences between the response signal and the interfacesignal to determine a quantitative cure state of the material.
 22. Amethod of claim 21, further comprising producing stable and reproduciblerelative reflection coefficient measurements of the cure material byusing the reflected response signal to correct and normalize thereflected interface signal.
 23. A differential ultrasonic waveguide curemonitoring system comprising: a differential ultrasonic waveguide curemonitoring probe comprising: an ultrasonic transducer for generating andsensing ultrasonic signals; a waveguide connected to and extending fromthe ultrasonic transducer, the waveguide for transmitting ultrasonicsignals; a reference for reflecting a reference signal back to theultrasonic transducer; a front face of the waveguide for contacting amaterial to be cured and forming an interface between the differentialultrasonic waveguide probe and the material to be cured, the interfacereflecting back an interface signal from the interface to the ultrasonictransducer; a computer coupled to the differential ultrasonic waveguidecure monitoring probe, the computer comprising: an input device forreceiving information relating to the reference signal and the interfacesignal; a processor for analyzing the information relating to thereference signal and the interface signal and for distinguishing thepropagation differences between the response signal and the interfacesignal to estimate the cure material modulus to determine a quantitativecure state of the material in a non-cure related signal variancesindependent calibrated response manner; a data storage device forstoring one or more of: the information relating to the reference signaland the interface signal, information relating to the material beingcured, and information relating to the cure process; an output devicefor outputting one or more of: the information relating to the referencesignal and the interface signal, information relating to the materialbeing cured, and information relating to the cure process.
 24. Thesystem of claim 23, further comprising: a signal gate for controllingsampling rate; an A/D converter; a pulser/receiver card for controllingpulse generation and receipt of the reflected signals; and a channelmultiplexer board for signal multiplexing.
 25. The system of claim 23,wherein the probe may be integrated into new computerized cure processmonitoring system
 26. The system of claim 23, wherein the probe may beretrofit into existing materials processing assemblies.
 27. The systemof claim 23, further comprising tooling mounting options for couplingthe differential ultrasonic waveguide probe to the material to be cured.